[clang ubsan failure] descriptor.cc calls memset(NULL) when lazily-loading descriptor with no dependencies

[jmillikin-stripe]

This was discovered in the Envoy test suite (envoyproxy/envoy#1682).

Given the following test body:

envoy::api::v2::Bootstrap bootstrap;
std::string bootstrap_text;
ASSERT_TRUE(::google::protobuf::TextFormat::PrintToString(bootstrap, &bootstrap_text));

Building with Clang 5 and -fsanitize=address,undefined will cause the test to fail with this error:

external/protobuf_bzl/src/google/protobuf/descriptor.cc:4167:12: runtime error: null pointer passed as argument 1, which is declared to never be null
/usr/include/string.h:62:62: note: nonnull attribute specified here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior external/protobuf_bzl/src/google/protobuf/descriptor.cc:4167:12 in 

descriptor.cc:4167 is a call to memset():

4160   result->dependency_count_ = proto.dependency_size();
4161   result->dependencies_ =
4162       tables_->AllocateArray<const FileDescriptor*>(proto.dependency_size());
4163   if (pool_->lazily_build_dependencies_) {
4164     result->dependencies_once_ = tables_->AllocateOnceDynamic();
4165     result->dependencies_names_ =
4166         tables_->AllocateArray<const string*>(proto.dependency_size());
4167     memset(result->dependencies_names_, 0,
4168            sizeof(*result->dependencies_names_) * proto.dependency_size());
4169   } else {
4170     result->dependencies_once_ = NULL;
4171     result->dependencies_names_ = NULL;
4172   }

If proto.dependency_size() is 0 and lazy building is enabled, tables_->AllocateArray(0) is called (returning NULL) .

[jmillikin-stripe]

This is fixed now.